1. Field of the Invention
This invention generally relates to an antenna apparatus, and more particularly to a dual-band planar monopole antenna for use in a wireless local area network (WLAN) system.
2. Description of the Related Art
With the development of the communication industry in recent years, various communication products have been developed for different applications. In particular, wireless local area network (WLAN) products have been growing rapidly, and antenna designs adaptable to industrial standards are in a great demand. In conventional techniques, most antennas are capable of operating only in a single band, either 2.4 GHz or 5.2 GHz in WLAN devices, and the antennas typically require additional matching circuitry for matching the antennas such that the cost of the antennas inevitably increase. As the market allows the coexistence of both bands (2.4 GHz and 5.2 GHz), it is desirable to design a dual-band antenna that can be operated in the 2.4 GHz and 5.2 GHz bands for a WLAN system.
Accordingly, the present invention provides an antenna which is simple in structure, low in manufacturing cost, and operated in dual-band mode so as to meet the requirement of the application in WLAN system.
It is an object of the present invention to provide a dual-band planar monopole antenna which can be operated in a dual-band mode for a WLAN system.
It is another object of the present invention to provide a dual-band planar monopole antenna which is light in weight and small in size for being easily adapted to a WLAN product.
It is a still further object of the present invention to provide a dual-band planar monopole antenna, wherein the antenna""s radiation pattern in the azimuth plane is substantially omnidirectional so as to suitably apply to the base stations or access points of a WLAN system.
In order to achieve the above objects, the present invention provides a dual-band planar monopole antenna, which is printed on a microwave substrate having a first surface and a second surface, wherein a radiating metallic element and a microstrip line are printed on the first surface, and a ground plane is printed on the second surface. The radiating metallic element has a stub portion, on which a feeding point is disposed, and a U-shaped slot, of which the opening facing the feeding point, for separating the radiating metallic element into a first sub-metallic element and a second sub-metallic element. The microstrip line is connected to the feeding point for signal transmission, and the ground plane printed on the second surface corresponds to an area of the first surface defined by the length of the microstrip line and the width of the substrate.